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排序方式: 共有178条查询结果,搜索用时 46 毫秒
101.
Jeanette Olli 《Geometriae Dedicata》2012,158(1):69-86
When dividing a 1- or 2-dimensional region according to a specified scheme, division points are continually created as the process continues. A measure results from assigning weights to each of these points. In the 1-dimensional setting, results concerning the distribution of division points are well known, and suggest how to study analogous processes in two dimensions. We explore two different division schemes on a triangular region and three different measures based on each subdivision, finding the limiting measures in each case. 相似文献
102.
Tadesse M Strøm MB Svenson J Jaspars M Milne BF Tørfoss V Andersen JH Hansen E Stensvåg K Haug T 《Organic letters》2010,12(21):4752-4755
Bioassay-guided fractionation of the sub-Arctic ascidian Synoicum pulmonaria collected off the Norwegian coast led to the isolation of a novel family of brominated guanidinium oxazolidinones named synoxazolidinones A and B (1 and 2). The backbone of the compounds contains a 4-oxazolidinone ring rarely seen in natural products. The structure of the compounds was determined by spectroscopic methods. The synoxazolidinones exhibited antibacterial and antifungal activities. 相似文献
103.
Van Emon JM 《Journal of AOAC International》2010,93(6):1681-1691
Foods are complex mixtures of lipids, carbohydrates, proteins, vitamins, organic compounds, and other naturally occurring substances. Sometimes added to this mixture are residues of pesticides, veterinary and human drugs, microbial toxins, preservatives, contaminants from food processing and packaging, and other residues. This milieu of compounds can pose difficulties in the analysis of food contaminants. There is an expanding need for rapid and cost-effective residue methods for difficult food matrixes to safeguard our food supply. Bioanalytical methods are established for many food contaminants such as mycotoxins and are the method of choice for many food allergens. Bioanalytical methods are often more cost-effective and sensitive than instrumental procedures. Recent developments in bioanalytical methods may provide more applications for their use in food analysis. 相似文献
104.
Cationic oxorhenium salen complexes are prepared by the abstraction of bridging oxo ligands with [Et3Si][B(C6F5)4] and [Ph3C][B(C6F5)4]. These complexes catalyze the reduction of 2-butanone with Et3SiH under ambient conditions. 相似文献
105.
Four rhodium dimers have been synthesized with a bridging diisocyanide ligand, dmb (2,2-dimethyl-1,3-diisocyanopropane): [Rh2(dmb)4](BPh4)2, [Rh2(dmb)4Cl2]Cl2, [Rh2(dmb)4I2](PF6)2, and [Rh2(dmb)2(dppm)2](BPh4)2 (dppm = bis(diphenylphosphino)methane). The complexes have been characterized by elemental analysis and mass spectrometry, as well as UV-visible, IR, and 1H NMR spectroscopies. X-ray crystal structures of the rhodium(I) complexes, [Rh2(dmb)4](BPh4)2 . 1.5CH3CN (3.2330(4), 3.2265(4) A) and [Rh2(dmb)2(dppm)2](BPh4)2.0.5CH3OH . 0.2H2O (3.0371(5) A), confirm the existence of short Rh...Rh interactions. The metal-metal separation for the rhodium(II) adduct, [Rh(2)(dmb)4Cl2]Cl2.6CHCl3 (2.8465(6) A), is consistent with a formal Rh-Rh bond. For the two luminescent rhodium(I) dimers and six previously investigated diisocyano-bridged dimers with and without dppm ligands, the intense spin-allowed dsigma-->psigma absorption band maximum shifts to longer wavelengths with decreasing Rh...Rh separation, and there is an approximate correlation between band energy and the inverse of the metal-metal separation cubed. Both [Rh2(dmb)4]2+ and [Rh2(dmb)4(dppm)2]2+ undergo oxidative addition in the presence of iodine. In the conversion of [Rh2(dmb)4]2+ to [Rh2(dmb)4I2]2+, the observed intermediate is tentatively assigned to a tetramer composed of two rhodium dimers. In the case of [Rh2(dmb)2(dppm)2]2+, no intermediate was detected. 相似文献
106.
From four Arnica species (A. angustifolia Vahl ssp. attenuata (Greene) Maguire, A. lonchophylla Greene ssp. lonchophylla Maguire (flowerheads), A. chamissonis Less. ssp. foliosa (Nutt.) Maguire, A. montana L. (roots and rhizomes)) a total of twelve lignans of the furofuran-, dibenzylbutyrolactone- and dibenzylbutyrolactol-type were isolated. No report on lignans as constituents of Arnica species exists so far. Besides the known pinoresinol, epipinoresinol, phillygenin, matairesinol, nortrachelogenin and nortracheloside, six dibenzylbutyrolactol derivatives with different stereochemistry and substitution at C-9 were isolated and their structures elucidated by NMR spectroscopic and mass spectral analysis. 相似文献
107.
The number of transversals in a Latin square 总被引:1,自引:0,他引:1
Brendan D. McKay Jeanette C. McLeod Ian M. Wanless 《Designs, Codes and Cryptography》2006,40(3):269-284
A Latin Square of order n is an n × n array of n symbols, in which each symbol occurs exactly once in each row and column. A transversal is a set of n entries, one selected from each row and each column of a Latin Square of order n such that no two entries contain the same symbol. Define T(n) to be the maximum number of transversals over all Latin squares of order n. We show that
for n ≥ 5, where b ≈ 1.719 and c ≈ 0.614. A corollary of this result is an upper bound on the number of placements of n non-attacking queens on an n × n toroidal chess board. Some divisibility properties of the number of transversals in Latin squares based on finite groups
are established. We also provide data from a computer enumeration of transversals in all Latin Squares of order at most 9,
all groups of order at most 23 and all possible turn-squares of order 14. 相似文献
108.
Stefano Lagomarsino Stefano Iotti Giovanna Farruggia Alessia Cedola Valentina Trapani Michela Fratini Inna Bukreeva Andrea Notargiacomo Lucia Mastrototaro Chiara Marraccini Andrea Sorrentino Ian McNulty Stefan Vogt Daniel Legnini Sangsoo Kim Alessandra Gianoncelli Jeanette A.M. Maier Federica I. Wolf 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(11-12):834-840
We report a novel experimental approach to derive quantitative concentration map of light elements in whole cells by combining two complementary nano-probe methods: X-ray fluorescence microscopy (XRFM) and atomic force microscopy (AFM). The concentration is derived by normalizing point-by-point the elemental (here Mg) spatial distribution obtained by XRFM, by the thickness measured using AFM. The considerable difference between the elemental distribution and the concentration maps indicates that this procedure is essential to obtain reliable information on the role and function of elements in whole cells. 相似文献
109.
Lopez-Garcia LA Schulze JO Fröhner W Zhang H Süss E Weber N Navratil J Amon S Hindie V Zeuzem S Jørgensen TJ Alzari PM Neimanis S Engel M Biondi RM 《Chemistry & biology》2011,18(11):1463-1473
Protein kinases are key mediators of cellular signaling, and therefore, their activities are tightly controlled. AGC kinases are regulated by phosphorylation and by N- and C-terminal regions. Here, we studied the molecular mechanism of inhibition of atypical PKCζ and found that the inhibition by the N-terminal region cannot be explained by a simple pseudosubstrate inhibitory mechanism. Notably, we found that the C1 domain allosterically inhibits PKCζ activity and verified an allosteric communication between the PIF-pocket of atypical PKCs and the binding site of the C1 domain. Finally, we developed low-molecular-weight compounds that bind to the PIF-pocket and allosterically inhibit PKCζ activity. This work establishes a central role for the PIF-pocket on the regulation of PKCζ and allows us to envisage development of drugs targeting the PIF-pocket that can either activate or inhibit AGC kinases. 相似文献
110.
Cathy McCullagh Jeanette M. C. Robertson Detlef W. Bahnemann Peter K. J. Robertson 《Research on Chemical Intermediates》2007,33(3-5):359-375
The use of semiconductor photocatalysis for treatment of water and air has been the topic of intense research activity over the past 20 years. This powerful process has also been extended to the disinfection of environments contaminated with pathogenic micro-organisms. This review summarizes recent developments concerned with the photocatalytic treatment of water contaminated with pathogenic micro-organisms presenting a potential hazard to animals and human beings. 相似文献